When supplying current to the stator of a rotating electric machine through a supply line from an inverter, the current flowing in the supply line is detected by providing a current sensor in the supply line.
U.S. Pat. No. 6,049,152 issued to Masaki Nakano on 11 Apr. 2000 discloses a composite motor provided with a plurality of rotating electric machines controlled by a single inverter. The single inverter supplies the composite motor with a composite current containing a plurality of current components having their respective frequencies. The respective frequency of the current component is determined in response to the rotational frequency of each rotating electric machine.